The invention relates generally to apparatus providing sliding surfaces enabling reciprocal movement between elements with low binding, wear and friction-forces. More specifically, the invention concerns intermediate sleeves for use between bearings, such as clutch release bearings, and a guide element extending through a bore in the bearing.
Requirements for increased fuel efficiency have prompted the transportation manufacturing industry to make increased use of lighter weight material such as aluminum in various parts of the vehicles being produced. Unfortunately, aluminum wears more readily than the cast iron or steel material that typically is replaced in various applications, and hence provision must be made in certain applications to minimize such wear. One particular application requiring such additional wear preventive measures is found where a conventional clutch release bearing having a steel bore now rides on a guide tube or quill made of aluminum. In such an application, one known approach to alleviating excessive binding, wear or excessive friction between the bore of the clutch release bearing and its aluminum guide tube is to place a sleeve having a low coefficient of friction in the bearing bore such that the sleeve on its inner surface will make sliding contact with the guide tube. Such sleeves are typically fashioned of a synthetic resin or plastic material and are often an integral part of the bearing carrier. Such known approaches, however, have been found to provide only a moderate degree of wear protection, in that, after a number of operating cycles, aluminum particles from the guide tube often become embedded in the plastic sleeve leading to aluminum particles sliding on the aluminum guide tube which, in turn, creates heavy friction forces and wear. Such friction increase may, in turn, lead to undesirable increases in the "pedal effort" needed to release the clutch in a manual transmission system.
None of the known art teaches, claims, or even suggests a sleeve having two sliding surfaces, either of which may be used to facilitate reciprocating movement between a bearing and its associated guide element.